Mostly portrayals of youth in medieval art was limited to the Madonna and child, with few exceptions. This was because most art in medieval times was religious based. As you can tell the Christ child was shown more as a miniature Man, with a fully developed body instead of a chubby baby. In the middle ages, perhaps because life span was shorter then, children were expected to work ad behave like adults at a young age. This concept was reflected In the art of that time period, showing youth as the adults they would soon be as opposed to the child that they were.